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  3. In the post-Silent Spring 1960s, when the pesticide DDT was discovered to be toxic to humans and wildlife and to persist for yea

In the post-Silent Spring 1960s, when the pesticide DDT was discovered to be toxic to humans and wildlife and to persist for yea

admin2016-03-10  91
问题     In the post-Silent Spring 1960s, when the pesticide DDT was discovered to be toxic to humans and wildlife and to persist for years in the environment, farmers and landscapers turned enthusiastically to Methoxychlor(甲氧氯). The pesticide—also commercially known as Chemform, Methoxo, Metox or Moxie—had a much shorter half-life and was billed as the safe alternative to DDT. Now, new research argues that exposure to the pesticide could cause diseases three generations later, in offspring who were never exposed to the Methoxychlor themselves. Biologist Michael Skinner and his team at Washington State University found that if a rat fetus is exposed to Methoxychlor during the first trimester(怀孕期的三个月)of pregnancy, the likelihood of kidney disease, ovary(卵巢)disease and obesity in their progeny(后裔)was elevated for three generations. Multiple diseases were even more prevalent in the third generation than in the second. In other words, Methoxychlor, which was banned in the U. S. in 2003 for a host of human health reasons, can still leave its mark on a population decades after exposure ends. The great-great-grandchildren of a woman exposed to Methoxychlor may still be suffering the consequences. The new finding follows Skinner’s previous research, which identified transgenerational epigenetic(遗传的)disorders resulting from toxins including PCBs and DEET through up to six generations. Epigenetics govern which genes turn on and off and when, so epigenetic "misbehavior" can lead to a range of diseases, especially obesity and diseases that affect the reproductive system and kidneys. In the majority of Skinner’s previous findings, the problem was identified as altered epigenetics in the sperm. In the Methoxychlor, it was the egg that contained the damaged "epigenetic signature" resulting in susceptibility to disease passed generationally through the mother.
    Methoxychlor was banned after it was found to mimic estrogen(雌激素), acting as a reproductive toxin leading to infertility in animals. It turned up in human breast milk, and it is assumed to be able to cross the placenta(胎盘). In high doses, it can act as a neurotoxin, damaging an animal’s nervous system. While those hazards would affect the first generation exposed, the epigenetic mutations that result from transgenerational inheritance can cause entirely different diseases. "If the sperm or the egg has an altered epigenetic signature that is being used to develop the early embryo(胚胎), those signatures are transferred to the embryonic stem cell, which can turn into any cell in the body. Because of the altered epigenetics, every cell in the body will have an altered expression of genes, and therefore so will every tissue," Skinner explained. "If the tissue is a type that is sensitive to small changes, to what genes are turned off and on, it will be susceptible later in life to disease. " For example, the adipose(脂肪的)tissue determines to a large degree how your body stores fat. Adipose is highly sensitive to epigenetic changes, like the kind that Skinner argues can be triggered by a great-grandmother’s exposure to Methoxychlor. If your adipose tissue is out of whack, even a small amount of caloric intake will be converted to fat, leading to obesity.
    The E. U. banned Methoxychlor in 2002, and the U. S. followed suit in 2003. But that doesn’t mean it immediately left the country’s food and water supply—a ban only ends production of the chemical, but any privately owned stocks of the chemical can still be in use, so banned chemicals can take years to be fully phased out. For example, the Environmental Working Group found above-threshold levels of Methoxychlor in some municipal water supplies in Iowa after 2004. While most developed nations have banned Methoxychlor, Skinner says the pesticide is still widely used in Mexico and in South American countries, where the U. S. gets a significant portion of its produce. Mexico is the second largest provider of agricultural products to the U. S. "If we get our food from places in South America and Mexico, that’s of concern," Skinner says.
Why are the offspring of people exposed to Methoxychlor more likely to develop obesity?
选项 A、Because they develop a strong desire for sugar and fat.
B、Because their bodies contain more fat tissues.
C、Because their fat tissues don’t function properly.
D、Because they consume calories more slowly than others.
答案C
解析 细节题。由题干中的obesity定位至第二段。根据该段后三句可知，受影响人群的脂肪组织功能出现异常，即使少量的卡路里也会被转化为脂肪存储在体内，从而导致肥胖，故答案为[C]。
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